PV vs Evacuated solar if you were curious

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(Simon) #21

Interesting. Wonder where Stephen got the idea that it was in mac address order?


(Robert Wall) #22

They will do. The order is defined by the serial number written into the sensor ROM at manufacture, it is totally deterministic (not random as has been asserted in the past) but the order is not evident on cursory inspection. The explanation of the search algorithm, which defines the order, has made it across into Learn, under Temperature Sensing.

As @cab123 says, hard coding the addresses into the sketch (or via EEPROM) avoids the difficulty when a sensor is not found and the remaining sensors shuffle down the order. (The new EmonLibCM - when it’s released - will have the ability to pre-load the addresses built-in.)

The DS18B20 doesn’t even have a MAC address! Maybe Stephen thought the ROM code looked sufficiently like one to call it that?

(stephen krywenko) #23

@robert --yes it looks like a MAC address to me if but a few hexadecimal longer.

@cal sure seams lower to higher when I look as the ROM address and the order they pop in - but no worries.

(Simon) #24

Yes should have said rom id or code.

But Robert weren’t you the one back then saying it was random and the only way to really know was to get the rom code/id and use this to determine what was what.

Anyway - I’m off to check out the new learn section to learn something new. :slight_smile: Thanks for the pointer.

(Simon) #25

Reply to myself!

Nice one - now I’m absolutely certain they’ll always be in the same order unless one has gone awol.

Thanks for pointing us there.


(Robert Wall) #26

I might have said that it appeared random, but I doubt that I actually said that it was. Unless you can transpose hex (bit reversal) in your head, I can safely say that it still appears random.

(MasterCATZ) #28

Thanks heaps for this

I am planning on Building a solar thermal system with around 60 sqm roof space

how ever I am wanting to use the heat for making electricity and not heating

(Lee) #29

Now that’s a crazy I’m interested in! Tell us more!

(stephen krywenko) #30

I often thought of trying that. by using peltier modules … they have simular efficiency as a PV of 15% but as high as 40% … but solar evacuated tube naturally track the sun better so you probably end up with 30% more power per square foot then a fixed PV if using common peltiers modules (15%)… peltier modules and some simple hydrodronic system you could probably heat and produce electricity … bumping up it overall efficiency to I think in 60% - 75% for usable energy extraction… depending on time of year.

how I thought of trying was a large collection of evacuated cells. in around 5 times what I need to produce my hot water needs input temp 80 -90c. once it goes through the hot water tank ( exit temp 75c) - it would go through - 10 kw grouping of peltiers modules ( which are cooled via a closed loop ground loop 10c) - exit temp 25-30c and if in house heating is required direct that though a high mass radiant floor exit temp 20 - 25C- to return to cycling through evacuated solar tubes again . where it heated to an exit temp of 80- 90 c again

but you are using 60sqm you can squish in 18 kw of thermals in that area which is about the longest continuous string recommenced for thermals . as that’s about 100c differential by the time the fluid enter and exits the system

(Doug) #31

My 2c worth…
I recently built 2 flats for persons with a disability. I used normal heater element HWS because I did not need to plumb water to the roof (costs$$$). Also I could place the HWS close to the place that used the water (next to the bathrooms, with a longer run to the kitchen). I redirect power from the 13Kw solar system which even though inefficient, is still cost effective. I got the solar system for a very very competitive price, & fitted 3Kw panels on East, & 10Kw on west. Limited to 5 Kw export, but still averaged 40Kw day export!
So, in my opinion, if a new build, fit as many solar panels as possible, & redirect power to the tank. (Applicable in Sunny Australia anyway!)

regards, Doug

(stephen krywenko) #32

i would agree with the current cost of solar panels it can be cheaper to use solar panels vs evacuated solar tubes as you can now get 1kw of solar panels for only 20% more then evacs – as you can have more usabe energy by the end of the day in the warm climate… i live in cold climate where I live I found it more advantageous to use evacs-- as I do not export and I built my system 12 years ago

where i gain my advantage in my area is heating and it pretty complex hybrid system - I live in generally a sunny location- for 6 month out of the year some form of domestic heating is required. hence why households consume - +35000 kwh per per year 20000kwh for heating 7000kwh for domestic water 7000 for everything else–

in the summer my excess is pushed into the ground which heats my soil to about 15 - 18c around my ground loop which boosts my heatpump to ~4COP ( normally it would be +3cop at 10c )
so i gain a fair amount my heat pump runs at an average of 3 COP for the entire season ( compared to 2.5 otherwise with out heating the ground loop) so i use 30% less energy on my heat pump because the overall COP is better-- the evacs heat my structure 66%. so i end up with heatpump reducing the average household 20000kwh by 66%= 6800kwh and the evacs reducing it again by 66% = 2300kwh per year to heat, from what normally would be +20000kw per year for a conventionally heated home… but sure in relations to the heatpump saved only 4500 kwh. during a period of low light . but if you consider the amount energy the evac dump into my soil added about 30% better efficiency on my heat pump over the season that comes out to about 5000kwh of extra energy that is extractable . so as a Battery the ground was not that bad - it actually seams to be a considerably positive gain value- i am guessing because it horizontal closed loop system. the extra energy being added from the evacs causing the soil to warm much faster and gain much more naturally added solar gain over the summer ( example when people work their ground loops surface black to gain 10 - 20% boost in their heat pump capacity because the sun heats the soil warmer and deeper over the summer . ) the only difference I am also heating mine from deep with in

(Doug) #33

I understand you have a special system in a colder climate. My comment as you said was for warm climates.
I am an ‘Energy Coach’ with Enova energy, voluntary position, with Enova being our local community owned energy retailer. I have been saying for some time that solar PV panels are cheaper than a ‘wet’ solar HWS. In our warm climate, it is usually more of an issue cooling than warming. Unfortunately, Australian homes are generally badly designed compared to European houses. We are coming around, but it will take some time.
regards, Doug

(stephen krywenko) #34

no worries–
i am still not sure why is more expensive though – simpler maybe but not cheaper
1kw of solar panels is currently about <30cents a watt FOB from china GTI usually equal to or greater than the cost of the panels- for a small system
so say 2kw that would cost FOB $1200 panel and gti (hotwater tank and diverting system not included ) but I can not buy solar panels from china any more in Canada as they placed a 250% tariff on them so if based on Canadian manufacture panel price that prices goes up significantly to FOB +60 cents a watt for solar panels from <30cents I use to pay – $2400

evacuated Solar Tubes --I can still import these with no tariff
1 kw evacuated solar is <20cents a watt FOB … controller for it is <$50, 1 pump I usually paid $22 for the pump and 200- 500$ for the tank( size dependent). … I setup the evacuated in low or zero pressure setup( no need for expansion tank). it consists of a thermal check valve a 2- 4 gallon tank that sits above the evacuated solar tubes - if the pump stops, the thermal relief opens creating a natural convection naturally “cooling” the system.- ( it can usually handle up to 4kw of thermals in series ) - then for line I can use PEX 3-4 feet after or before the thermals . cost wise is cheaper for the evacs as that would be about <$900 FOB everything including controller, 2 pumps. fill tank water lines, hotwater tank ( which was not include in the solar panel setup) 1 gallon polypropylene glycol …etc from my last import query – so not sure why it would be more expensive in Australia

(Doug) #35

Ok, so in Australia, atm we get rebates on both SolarPV & Solar HW. The reason PV works out cheaper for us, & a TCO issue too: The plumbing costs for a roof mounted ‘wet’ system are far more than adding a few panels to the size of a SolarPV system (at total installation time). I understand ‘wet’ systems are far more efficient, but for an average house installation in Australia, PV + storage tank is much cheaper, added to which the maintenance costs are lower for PV + storage tank.
To give an idea of PV system cost in Australia, I just fitted 13Kw (+ 1.5Kw of recycled panels) with 2x 5Kw Solar Edge inverters with Optimisers for less than $Au14K installed. (52 panels, 46 or 295w & 6 recycled 250w panels) The panel rebate reduces soon (which is one reason I updated my system). The cost will probably increase by 10% then.
To install a ‘Wet’ HWS for a 4-5 person house including plumbing in Australiab probably costs about $Au6K. (315L tank & 2 panels, or 24 vacuum tubes)

regards, Doug
On my house, I have an old ‘wet’ solar system, now 20yo. Irecently changed my roof after a major hailstorm. The collector panels were u/s, but the Stainless roof mounted tank was fine (because we use rain water & low pressure with a Gravity feed system). It was a toss up if I actually changed the system, but I decided to keep it, using new (absorption) collector panels.

(stephen krywenko) #36

okay - 6k eek that a hefty markup the same type of system here 24- 36 tube ( 2 kw) is ~2.5KCAD- installed ( after rebate 1.5k) --they install as pressurized system usually.
we currently do not have any rebate system for alternative energy( we did for a couple years but the new government cancels them all last year ) – but i do not know about you but i always found government rebate systems always to turn slowly into a massive gravy trains – as installers/retailers jack prices 30- 100% and what ever the rebate was equal to they rise the price of the install to match so the consumer pays just as much as before the rebate came into effect after a little while. And the installers/retailers sit on the gravy train while it lasts ( as the government footing 30-50% of the bill) .I’ve seen this happen time and time again - it just the rebate(incentive) system did not last very long for it to happen this time around for alternative energy installs to reach momentum - which was sad people were just starting to make the big push into going green… now it stopped again

(Doug) #37

yes, the ‘wet’ HWS are expensive. Also there is a rort with on-going maintenance where in some systems, the sacrificial anodes must be changed for on-going warranty (There have been instances where the anodes are only cleaned, but the customer is charged for new ones: very hard to police).
The rebate on Solar PV has always worked well in Australia because the market is so competitive. Even so, there are rogue retailers who sell below-average equipment to unsuspecting consumers.
Also the rules change: now the Electricity retailer ‘owns’ the meter, so if a meter change is required to finalise installation of a solar PV system, sometimes the retailer drags their feet for the meter installation. Hard to prove, but financially in the interests of the retailer to be slow. Unfortunately, there will always be companies that play the system in their own interests.
All we can do as consumers is to try to get the policies to be fairer. (One reason I go to the C4CE (Coalition for Community Energy) forums held every 4 years for instance. We do what we can.

btw, the Aussie Pollies in power are far worse than virtually any other country. We have ultra-conservatives currently pushing to have Sustainable energy wound down, with the moderates wanting change, so the result is nothing is done. The School students are even rallying about climate change, but no-one seems to be listening (some of these students will be voting next year, so the pollies ignore at their peril I feel, but still deaf ears!)
So, we do what we can…

In the meantime, you do your sums & install what you can afford. Hopefully the sales person does not sell you a dud if you are an ‘average’ consumer. (One of the reasons I am an ‘Energy Coach’ with our local Community owned retailer called ‘Enova Energy’.

This is all getting a bit off topic, so if this conversation cntinues, we should move it to a more suitable stream.

regards, Doug

(stephen krywenko) #38

no worries-- But I think your market is over charging on the wet “HWS” as in Canada or in my province specifically --provincial approved system and vendor installed with out rebate are only 2.5k…Anode issue — are not your tanks glass lined??. now alot of them are carbonfiber/fiberglass. and if you use good fitting and PEX you’re good for +25years ( I believe my current hot water tank is something like +30 maybe 40 years old as bought it used to build my hybrid heating system ( will out live the 0.4mm evacs systems as the heat transfer pipe has about + 15 year lifespan— I suggest “wet-HWS"when ordering get the 0.8mm heat transfer pipe they are slightly less efficient but will last practically forever as they do not suffer expansion fatigue as the <=0.4mm will that where you get the premature failure from. if you have the <=0.4mm heat transfer pipe you can extend the lifespan indefinitely by buying 304 stainless steel tubing cut to 4 - 6” length and insert them on the tip of the heat transfer pipe… I being working with, installing evac tubes and importing systems in Canada since 2005… I ran into probably every type of install usage issue there is - the only maintenance i ever had personally is changing pump ( but I was experimenting with different pump types - the best pump is a wobble pump but it very difficult to fine them- very low power with positive displacement ), adding antifreeze or change a gas tube as someone shot one on my house from a stray bullet oh yeah and exploding heat transfer pipe but my climate way to cold for 0.4mm the manufacture replaced them all for free - 300lbs of 0.8mm heat transfer pipes as they sent me the wrong ones – these guys make really nice ones at a good price Bluesun Solar Energy Tech. Co., Ltd also provide 0.8mm tubing ~$230 with roof mounts and reflectors 18 tube 1800mm unit $288 for a 24

yeah Australia going to be hit hard by climate change-- your own government estimates put your temp rise at between 4-6 c by the end of the century( that was 5- 7 years ago - today i suspect it much higher then that estimate )

but any ways have a great day
ps here a picture of my last quote from them